linux-kernel - Re: [PATCH Part1 RFC v4 15/36] x86/mm: Add support to validate memory when changing C-bit

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Message-ID: <c7e917be-ef01-3eeb-0e74-d94fef834cb0@amd.com>
Date:   Tue, 17 Aug 2021 13:18:44 -0500
From:   Brijesh Singh <brijesh.singh@....com>
To:     Borislav Petkov <bp@...en8.de>
Cc:     brijesh.singh@....com, x86@...nel.org,
        linux-kernel@...r.kernel.org, kvm@...r.kernel.org,
        linux-efi@...r.kernel.org, platform-driver-x86@...r.kernel.org,
        linux-coco@...ts.linux.dev, linux-mm@...ck.org,
        linux-crypto@...r.kernel.org, Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Joerg Roedel <jroedel@...e.de>,
        Tom Lendacky <thomas.lendacky@....com>,
        "H. Peter Anvin" <hpa@...or.com>, Ard Biesheuvel <ardb@...nel.org>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Sean Christopherson <seanjc@...gle.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Andy Lutomirski <luto@...nel.org>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Sergio Lopez <slp@...hat.com>, Peter Gonda <pgonda@...gle.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Srinivas Pandruvada <srinivas.pandruvada@...ux.intel.com>,
        David Rientjes <rientjes@...gle.com>,
        Dov Murik <dovmurik@...ux.ibm.com>,
        Tobin Feldman-Fitzthum <tobin@....com>,
        Michael Roth <michael.roth@....com>,
        Vlastimil Babka <vbabka@...e.cz>, tony.luck@...el.com,
        npmccallum@...hat.com, brijesh.ksingh@...il.com
Subject: Re: [PATCH Part1 RFC v4 15/36] x86/mm: Add support to validate memory
 when changing C-bit



On 8/17/21 1:17 PM, Borislav Petkov wrote:
> On Tue, Aug 17, 2021 at 01:07:40PM -0500, Brijesh Singh wrote:
>>>> +	if (!desc)
>>>> +		panic("failed to allocate memory");
>>>
>>> Make that error message more distinctive so that *if* it happens, one
>>> can pinpoint the place in the code where the panic comes from.
>>>
>>
>> Now I am running checkpatch and notice that it complain about the message
>> too. I can add a BUG() or WARN() to get the stack trace before the crashing.
> 
> checkpatch complains because there's a kmalloc before it and if it
> fails, the mm core will issue a warning so there's no need for a warning
> here.
> 
> But in this case, you want to panic and checkpatch doesn't see that so
> you can ignore it here and leave the panic message but make it more
> distinctive so one can find it by grepping. IOW, something like
> 
> 	if (!desc)
> 		panic("SEV-SNP: Failed to allocame memory for PSC descriptor");
> 

Got it, I will update the message accordingly.

thanks